Issue

FFUs: Setting a course for energy efficiency

09/01/2004

Development of a testing standard for fan filter units will go a long way in improving energy efficiency in cleanrooms

BY SARAH FISTER GALE

In the past five years, Fan Filter Units (FFUs) have rapidly replaced distributed air handling units and fan tower systems as the airflow technology of choice in new and retrofitted cleanroom environments.

The FFU, which consists of a small fan, a controller and a HEPA/ULPA filter enclosed in a box, maintains specific airflow, and is commonly installed directly into the ceiling grids.

The reason they've gained such popularity is that FFUs provide a relatively simple means of delivering filtered air to environments requiring high degrees of cleanliness. Smaller and more portable than traditional airflow systems, FFUs cost less to install, are more flexible and can be focused in targeted areas of a cleanroom environment for maximum performance without excess redundancy.

Unlike traditional recirculating air fans often used in cleanroom systems, such as larger plug or centrifugal fan units or vaneaxial fan systems, FFUs can be added easily to existing cleanrooms without major retrofitting. The compact FFU system makes it possible for owners to update contamination control systems in cleanrooms as their needs and the standards change, without having to raise the roof or tear down walls. They also can be easily mounted directly over key equipment or above workbenches to create temporary portable cleanrooms within manufacturing environments.

Airflow systems are energy gluttons

While FFUs are more efficient than traditional systems, even these smaller airflow units consume a significant amount of energy, adding to the already overloaded energy consumption rates of most manufacturing facilities. Due to the high air circulation rates and special environmental considerations, cleanrooms consume from 4 to 100 times more energy per square foot than conventional commercial buildings. As energy costs increase and power grids get overloaded, meeting higher energy efficiency goals and reducing energy use has become a serious priority for cleanroom facilities.

Within those environments, FFUs are a specific concern because they are an energy-intensive component of energy-intensive industries, according to Dr. Tengfang (Tim) Xu, project manager in the Environmental Energy Technologies Division of Lawrence Berkeley National Laboratory (LBNL; Berkeley, Calif.).

FFUs have become the poster child for improving energy efficiency in cleanrooms, winning interest and investment from high-profile groups, including LBNL, California Energy Commission and industry associations intending to improve cleanroom efficiencies. Much of the quality of "clean" in a cleanroom depends on the number of FFUs, and the filter types—high-efficiency particulate air (HEPA) or ultra-low penetration air (ULPA)—without which a cleanroom is simply a room. The lower the cleanliness class number the more FFUs are necessary to clean the air.

To meet Federal Standard 209(E) for Class 10 or Class 1 environments, a cleanroom will incorporate FFUs in every 0.6- to 1.2-m ceiling bay. These environments then have a laminar flow of clean air traveling downward at about 27.5 meters per minute, which ensures a positive pressure inside the cleanroom. The pressure blocks any influx of contaminants through leaks in the cleanroom wall or curtain, and guarantees that particles generated by people or process equipment inside the enclosure are quickly removed.

The airflow systems in facilities with cleanrooms drive an estimated 50 percent or more of the total energy use, with fan energy use accounting for 80 percent of total energy use in cleanrooms of ISO Classes 3, 4, or 5, which are the most electricity intensive.

The good news is that there are many opportunities for improvement, according to Xu. "Optimizing aerodynamic performance in air recirculation systems appears to be a useful approach to improve energy efficiency in cleanrooms."

The cutaway shows typical fan filter unit components.

Click here to enlarge image

Larry Hopkins, engineering manager for Huntair (Portland, Ore.; www.huntair.com), a manufacturer of high-performance airflow systems, agrees. "When FFUs first came on the market price was the biggest selling point followed closely by noise control," he notes. As a result, manufacturers made design choices to push costs down, and added sound blocking elements that restricted airflow. "They ended up with very inefficient models," he says.

What end users didn't realize was that the cheaper models cost far more to operate because they required so much more power to produce the same level of airflow as the more efficient designs. For example, an energy-inefficient two-by-four FFU uses roughly 300 watts of power whereas an energy-efficient model may cost $100 more but could use as little as 50 watts. The up-front investment pays for itself in energy savings in as little as eight months (based on savings of 250 watts and 7 cents/kWh).

Computational Fluid Dynamics (CFD) analysis of an inefficient FFU (top) and a next-generation FFU (bottom). Areas in red show resistance to air flow.

Click here to enlarge image

Huntair engineers tested several FFUs on the market to evaluate areas for improvements and were surprised by what they found. "The possibilities for improving energy efficiency on fan wheels alone is shocking," Hopkins says. The problem is that suppliers have been using the same general FFU design since the 1990s, and, because the original designers did not prioritize energy efficiency, it is difficult to make these kinds of improvements. Hopkins believes that FFU efficiencies would increase tremendously if engineers started their redesigns from scratch. "If you add more-efficient motors, better fan wheels and change the design for noise control, you can develop a highly efficient FFU."

Standards will drive better performance

Cleanroom owners are showing more interest in improving their energy performance, which is a good start, Xu says. However serious efficiencies won't be achieved until suppliers have a way to uniformly measure FFU energy consumption so that product comparisons can be made.

Today most FFU suppliers include performance test data regarding the noise, vibration and energy performance of their units with the product, but those numbers are impossible to validate. They are generally based on in-house tests that may have been conducted in empty isolated labs or warehouses that have little correlation to performance in a cleanroom. Even if the tests are relevant and accurate, there are no criteria to benchmark test data or decipher the test data as it relates to how it will operate after installation.

"None of the suppliers share test methods so there is no way to compare performance across the industry," Xu says. "The industry needs a consistent and valid way to report test numbers."

The first step, says Xu, is developing a set of standards to establish guidelines for testing FFU models. "To achieve high-efficiency FFUs, a standard test method needs to be developed for valid comparison."

Xu is currently vice-chairman of IEST working group 36, which is authoring a set of standards called "A Laboratory Method of Testing Energy Performance of Fan-Filter Units." The test standard is developed by LBNL, in collaboration with the Industrial Technology Research Institute (ITRI) of Taiwan and members of the Project Advisory Committee (PAC) for the high-performance building project supported by the California Energy Commission. "This project is a good start toward making the tool available and to gain industry's acceptance of the same document," he says. "Using this standard, we can investigate the effects of various designs among different manufacturers. We can also produce baseline information through testing the FFUs in the market or under development."

When the standards are complete, they will provide a uniform test procedure for laboratory characterization of FFUs by determining energy performance in terms of unit airflow rate, static pressure, electrical power usage, and total pressure efficiency. The object of the program is to provide a method for performance testing and reporting based upon consistent procedures. If the set of standards for FFU testing is approved, it will give suppliers a verifiable set of test procedures by establishing guides for third-party audits of FFU performance. This can then be referenced by and integrated into a relevant industry recommended practice.

In creating the standards, the IEST Working Group dealt with many testing issues, such as what the best testing methods would be, how airflow rates would be measured, and the impact of measuring vertical versus horizontal installations. There were many choices to be made, but fortunately there were few conflicts. "We are all in high degree of agreement on the standards tests," Xu says, noting the industry's excitement and enthusiasm to push the standard forward.

The first draft of the document has been under public review since April, 2004, and is being fast tracked by IEST. "The feedback has been overwhelmingly positive," Xu says. "Everyone in the industry wants a standard. This is a universal issue." He expects the final draft to be available soon on the LBNL publication Website (www.lbl.gov/publications) and that hopefully it will be integrated into IEST's standard some time in the near future.

Suppliers gain credibility, users save money

When the standard passes, experts agree that everyone in the industry will gain some value.

Suppliers will benefit because a standard for testing gives them more credibility, says Paul Christiansen, director of sales for Envirco (Albuquerque, N.M; www.envirco.com), an FFU manufacturer. Envirco began working on energy-efficient FFUs five years ago to meet demands from clients in Asia who had stricter energy usage guidelines. According to Christiansen, the company's most successful energy-efficient FFU, the Mach 10 IQ, features a DC motor that uses 20 percent of the power of an AC motor, lowering its energy consumption to 80 watts. Christiansen also notes that in the past three years U.S. companies have begun making similar demands, increasing the popularity of the Mach 10 nationally.

Many other FFU suppliers have already begun offering more efficient FFUs, recognizing the growing demand from U.S. consumers. Along with Envirco and Huntair, Terra Universal (Anaheim, Calif.; www.terrauniversal.com) Airguard (Louisville, Ky.; www.airguard.com),

These FFU makers are all anxious to see the standards move forward so they can verify the validity of their test data and validate the efficiency ratings of their units. Several of the suppliers, including Envirco, are participating directly in the IEST working. "We are 100 percent behind the standard," Christiansen says. "It will level the playing field for test procedures."

A new standard will also provide the industry with a benchmark for continuous improvement and gives suppliers a way to establish a competitive edge by comparing their efficiency rates to other FFU manufacturers in the industry, says Patsy Dugger, industrial and agricultural program manager for the Savings by Design program at Pacific Gas and Electric (PG&E), California's energy utility company. "Rated, tested efficiency is a valuable marketing tool in a time when customers are increasingly paying attention to utility costs."

End users will benefit, because they will finally have reliable consistent test data so they can compare the efficiencies of products across the market, adds Hopkins. Right now, companies either have to select an FFU model and hope for the best, or perform their own in-house evaluations, which is time intensive and expensive. "The IEST standard is absolutely needed," he says. "You can't make an informed decision without reliable test data."

Once the standard is in place, Hopkins predicts that many sophisticated buyers will start making buying decisions based on energy costs, which will drive design changes across the market. "Once the standard is in place, specifiers will demand more efficient models and that will push manufacturers to make design improvements if they want to stay competitive."

California leads the charge

Besides suppliers and buyers, the push for change in the industry will benefit the communities where manufacturers are based because overall energy consumption rates will drop, lessening the burden on power grids and enabling them to put off building additional power plants, notes Dugger. This is especially critical in California, where high tech manufacturing has a huge presence and the state is battling an ongoing energy crisis.

The California Energy Commission (CEC) has prioritized reducing energy consumption in cleanrooms, and has put 'improvements in FFU performance' at the top of its list. "This could have a significant impact on public utilities in California," says Tony Wong, senior mechanical engineer for the CEC. "If manufacturers reduce their energy consumption it could help manage the grid and reduce power outages."

According to Paul Roggensack, the program contract manager of CEC, the CEC initially granted about $120,000 to this project to develop the draft FFU testing standard with the hope that it will spur more interest from the manufacturing industry in energy issues. CEC has a Public Interest Energy Research (PIER) program that supports public interest energy research, development and demonstration (RD&D) that helps improve the quality of life in California by bringing environmentally safe, affordable and reliable energy services and products to the marketplace (www.energy.ca.gov/pier/index.html#indust). The current FFU testing standard project is supported by the Industrial/Agricultural/Water End-Use Energy Efficiency program, which generally develops and demonstrates new technologies in this sector that increase energy efficiency and reduce emissions and manufacturing costs for California industries, agriculture and municipal water and wastewater systems. "Our goal is to reduce energy consumption and all studies focus on air systems as the primary target," Wong and Roggensack say.

Choosing more efficient FFUs will also contribute significantly to achieving energy reduction goals set forth in the 2000 Technology Roadmap for High-Performance Laboratories and Cleanrooms, produced by LBNL in conjunction with CEC and PIER. The goal is to achieve 50 percent reduction in building energy use for comparable production in new construction while maintaining or improving productivity and safety by 2012.

To further incent end users to make more energy-efficient choices, PG&E is working with LBNL and the CEC to develop rebate programs for manufacturers. The utility has two programs—the New Construction Savings By Design and the Retrofit Standard Performance Contract—that could potentially offer incentives for installing efficient FFUs. In both programs, the incentive is based on the annual calculated energy savings over what is considered the program baseline. 700,000 kWh annual energy savings would be multiplied by the incentive rate for process systems, 0.10/kWh, to determine a potential incentive of $70,000, which would be paid after project completion.

"PG&E is very interested in being able to offer incentives for efficient FFUs," Duggan says. "It is more cost effective for us to pay for a "nega-watt" through energy efficiency programs than it is to pay for a megawatt through generation." The program would increase the benefit to customers who get the energy and cost savings of efficient equipment for the life of the equipment, and they can take advantage of utility incentives, which can buy down higher first costs. "Cleanrooms are increasingly looking for new methods and equipment to save energy in their production facilities. We're hoping that those who are not aware of potential energy and utility savings will be further educated through the expansion of our programs."

But the programs can't be launched until the standards are established. "Before we can justify paying customers for using a certain piece of equipment, it would need to be tested for its operational efficiency and compared to other units." The utility is awaiting approval of the FFU draft test procedure and is working with LBNL and the CEC to develop performance data on FFU performance before it launches the program. It is working directly with LBNL engaging FFU manufacturers to test unit performance so they can establish a baseline of test data for the program. "Once a critical mass of FFUs have been tested and we can establish a range of efficiencies, we can start to pay for the high-performance units," Dugger says.

Every manufacturer that participates in the testing receives free test data regarding their products and their data remains anonymous in the final report, Xu says. "We are looking for industry's in-kind support to loan or give away units for our testing and for evaluating the test standard itself." The group is still looking for more participants and Xu encourages all FFU suppliers to contact him about getting involved (e-mail Tim Xu at ttxu@lbl.gov).

The future

Xu emphasizes that having a laboratory standard for FFU testing is only the first step toward improving energy efficiency in the industry, and that there is still so much more that should be done. "Having this draft standard in place is just the very beginning of what we hope to accomplish," he says.

Ideally, he'd like the standard to set off a domino effect in the industry. If the standard causes buyers to make more energy-efficient choices, that would encourage manufacturers to embrace best practices in cleanroom design and operation.

He hopes to find funding support in future FFU research, development and demonstration efforts that include conducting tests of additional FFUs of various types, with different controls, and different designs; resolving various technical issues surrounding refining the draft FFU testing standard such as airflow, uniformity, locations; and improving FFU designs through investigating factors contributing to actual performance levels, such as motor types, speed controls, housing, and fan wheel design. By working with IEST, he also hopes the industry will embrace a recommended practice guideline that will be accepted globally.

"Looking forward, I see that improving energy efficiency of FFUs has significant impacts on the energy market and the way suppliers and users would treat it."

Noise and vibration—still issues

No matter how energy efficient an FFU is, end users will still demand compact units that create the lowest amount of sound and vibration in the cleanroom environment. "Cleanroom tools are extremely sensitive to noise and vibration," says Michael Gendreau, president of Colin Gordon and Associates (San Bruno, Calif.), an acoustics and vibration consulting company specializing in high tech facilities. From a vibration standpoint, FFUs are more desirable than traditional airflow models because they have smaller motors, but noise is a bigger problem. Because the units are compact there is little room within the unit to reduce the amount of sound it generates.

Most FFU manufacturers provide noise and vibration test information, however it's isolated data that doesn't take into account the specifics of the cleanroom environment. The acoustic performance of an FFU is best described by the outlet sound power, which represents the portion of the acoustic energy emitted into the workspace of a cleanroom.

"You have to determine how that will translate to your environment," Gendreau says. "One FFU tested in a lab is very different from one installed in a crowded cleanroom where there is little absorption and a lot of reverb."

Further complicating matters is the changing decibel level in cleanrooms. As cleanrooms age and more equipment is added, sound levels will gradually increase until it becomes an intolerant work environment for staff or causes damage to noise-sensitive equipment. FFUs become louder when their HEPA filters clog or fans fall out of balance, which means regular monitoring of units is also critical to maintain minimum noise levels.

Often end users have to make choices between efficiency, noise and cost, says Larry Hopkins, engineering manager for Huntair (Portland, Ore.; www.huntair.com), a manufacturer of high-performance airflow systems. FFU makers reduce noise by adding insulation and pans to block or absorb sound. "The added material reduces the noise, but it restricts airflow so much it chokes the fan and requires more power to pump the same amount of air."

However, sometimes energy efficiency and noise reduction can work together in FFU installations—if good up-front investigation is done. Gendreau worked with a company that was able to reduce sound levels in its facility by installing twice as many FFUs and running them at half speed. Because the lower speed caused less wind drag, the energy costs dropped as well. "There is always a trade off," he says of the cleanroom design. "The best thing is to find that middle ground."